Printers have become exceedingly popular peripherals for computers and other types of computerized devices. They enable users to print images onto media, most commonly paper. There are many different types of printers, including most popularly inkjet printers and laser printers. Inkjet printers generally operate by ejecting fine droplets of ink onto the media, whereas laser printers generally operate by fusing toner onto the media. Either type of printer may be a black and white-only printer, or a color printer.
For color printers in particular, a color space conversion is usually performed on an image prior to its being printed. A color space is a color model that is used to represent the colors of an image. The typical color space for display purposes is red-green-blue (RGB), whereas a type of color space used for printing purposes is cyan-magenta-yellow (CMY). By combining the constituent colors of a color space in different ways, any desired color can be represented. Depending on the color model being used, combining the constituent colors of the model produce different results.
For example, the RGB color model for a display, such as a cathode-ray tube (CRT), specifies a given color as varying intensities of red, green, and blue. White is specified as the highest intensities of red, green, and blue, whereas black is specified as the absence of red, green, and blue. The CMY color model for a printer similarly specifies a given color as varying intensities of cyan, magenta, and yellow. However, black is specified as the highest intensities of cyan, magenta, and yellow, whereas white is specified as the absence of cyan, magenta, and yellow. For quality, economy, and other reasons, black ink is usually also used, such that the typical color space for printing purposes is in fact cyan-magenta-yellow-black (CMYK).
Conversion of a color value from an RGB color model to a CMY, CMYK, or other color model typically employs a three-dimensional look-up table (LUT). For each unique combination of red, green, and blue color values, the table provides corresponding values for cyan, magenta, yellow, and black. The table is three dimensional in that three different color valuesxe2x80x94the red value, the green value, and the blue valuexe2x80x94dictate the corresponding values for cyan, magenta, yellow, and black. Once all the pixels of an image are converted from RGB to a given printer""s resident color model, printing may occur.
Constructing a multi-dimensional LUT, however, can be quite laborious. Simply constructed LUT""s may be used for basic printing, but to ensure high quality printing, more elaborate methodologies are employed for constructing LUT""s. Because of the vast number of entries in a typical three-dimensional LUT, a method for constructing the LUT may start with a number of manually determined key or significant points, referred to as control points, and the remaining points are interpolated from the control points. Although this assists LUT construction somewhat, there can still be as many as four-thousand or more control points that have to be manually set, meaning that LUT construction is nevertheless still labor intensive.
For these described reasons, as well as other reasons, there is a need for the present invention.
The invention relates to determining the control points for constructing a lookup table from a first color space to a second color space. Black and white control points are determined based on an allowable total colorant amount and an absence of colorant, respectively. Control points between the black control point and the white control point are determined. A primary control point is determined for each of a number of first and secondary primary colors of the first and the second color spaces, based at least on the allowable total colorant amount. Control points between the white control point and the primary control point for each primary color are also determined. Finally, control points between the black control point and the primary control point for each primary color are determined.